Field of the Invention
The present invention relates to a sheet stacking apparatus configured to form a plurality of sheets conveyed from an image forming apparatus into a bundle of sheets and move the bundle of sheets, and to an image forming system including the sheet stacking apparatus.
Description of the Related Art
Hitherto, there have been provided image forming systems in which image forming apparatus such as a copying machine, a printer, a facsimile machine, and a multifunction peripheral thereof are connected to post-processing apparatus configured to perform various types of post-processing including sorting, aligning, binding, folding, and perforating on sheets discharged from the image forming apparatus. Those post-processing apparatus are each configured to stack sheets from the image forming apparatus on a processing tray, perform necessary post-processing, and then convey the sheets onto a stack tray.
There has been known a post-processing apparatus having a sorting function of sorting sheets, without binding the sheets, and then discharging and stacking the sheets onto one stack tray (U.S. Pat. No. 6,241,234). In U.S. Pat. No. 6,241,234, there is described a sheet processing apparatus having a configuration in which, when the number of sheets included in one bundle of sheets to be discharged in a sorting mode is equal to or larger than a predetermined number, the bundle of sheets is divided into groups each including a small number of sheets, which is at least two sheets, and discharged to the processing tray, and after that, the bundle of sheets stacked on the processing tray is discharged to a stack tray by a bundle discharge roller.
In the above-mentioned related-art apparatus, there has been a concern in that, when the bundle of sheets is moved from the processing tray to the stack tray in a state of a bundle, a leading edge of the bundle of sheets may be brought into abutment against an upper surface of sheets aligned and stacked in advance on the stack tray to cause displacement of the sheets on the stack tray by the effect of a force of moving the bundle of sheets, with the result that a stack alignment property of sheets may be degraded.